That list contains lines from many price points.
NCL does not compare to Seabourn or Regents. Its also a very difficult question to answer without a LOT more information as to your price range and expectations of the cruise.

You are probably best of finding a travel agent that specializes in cruising so they can help find you a prefect cruise for you.

But, if you want us to help, we will need to know more about - what your price point is, what ports you feel you MUST see if any, what type of service do you expect on your cruise (Seabourn offers very individualize service at a price), Do you want to be cruising with others your own age, are you both very active people, when would this cruise be and do you have any preference on where the cruise leaves from?